1. Field of the Invention
The present invention relates to a digital camera on which a solid-state image pickup element having color detection pixels for R (red), G (green), and B (blue) and luminance detection pixels is mounted.
2. Description of the Related Art
A solid-state image pickup element which is mounted on a digital camera to take a color image has color filters of the three primary color R, G, and B that are arranged in, for example, the Bayer pattern. In a configuration in which only R, G, and B color filters are disposed, when the color of an object is biased, there is a problem in that the luminance resolution of a photographed image is impaired.
In order to solve the problem, JP-A-2003-318375 discloses a related-art technique in which, among pixels constituting a solid-state image pickup element, pixels in a checkered pattern position are used as luminance detection pixels, and R, G, and B color filters are formed on respective pixels in the other checkered pattern position, so that the luminance resolution of a photographed image does not depend on the color of an object.
In some of digital cameras on which a solid-state color image pickup element where luminance detection pixels are formed is mounted, when a motion picture is to be photographed, for example, reduced image data are read out from the solid-state image pickup element in order to enhance the frame rate.
Also JP-A-2003-318375 teaches a technique for reading reduced image data from the solid-state image pickup element. For example, image data are not read out from the luminance detection pixels, image data are read out only from color detection pixels having respective R, G, and B filters, and the image resolutions in both the vertical and horizontal directions are accurately reduced to ½.
In the case where reduced image data are read out from a solid-state image pickup element, when the reading is performed while pixels are decimated as described above, all photo data of the decimated pixels are wasted. In recent solid-state image pickup elements, the number of pixels reaches the limits of the technology, and the signal charge amount which can be received by one pixel is very small. When image data are read out from a solid-state image pickup element while decimating pixels, therefore, there arises a problem in that the luminance sensitivity is lowered.